Human pluripotent stem cells (PSCs) are an exciting potential source of information about human development and disease, and may even allow for cell based treatments for today's incurable diseases. Thus far, however, the cells differentiated in vitro from PSCs do not faithfully represent naturally made cells by either gene expression or functional measures. Previous studies have demonstrated that many of these gene expression differences are related to the LIN28 proteins and the let-7 family of microRNAs that they regulate. By changing the expression of members of this LIN28/let-7 circuit in PSC-derived cells the discrepancies distinguishing them from cells made in vivo could be reduced. These changes could lead to the generation of more representative, potentially more clinically useful cells from stem cells. Using PSC-derived neural progenitor cells (NPCs), the tissue-specific stem cells of the developing nervous system, we propose to test the effects of LIN28/let-7 manipulations on gene expression and the differentiation potential of NPCs along their developmental timeline. Cutting-edge single cell analyses will also be used to determine how heterogeneous these cells are in vitro compared with their counterparts in the nervous system. Lastly, NPCs with LIN28/let-7 manipulations will be used to generate small brain-like cerebral organoids to investigate how large scale organogenesis is affected by the accuracy with which PSC-derived NPCs mimic those found in the developing brain. Our preliminary data implicate the LIN28/let-7 circuit and downstream targets in the transition from early neurogenic NPCs to older NPCs that primarily generate glial cells. This research will shine new light on the degree to which stem cell differentiation can mirror development, and has the potential to improve the generation of therapeutically relevant stem cell derivatives. Together, these developments may accelerate the translation of promising stem cell treatments from the research bench to the clinic.